Semiconductor device having ferroelectric substance capacitor

ABSTRACT

The invention provides a semiconductor device having a ferroelectric substance capacitor small in the occupying area and large in capacitance and a semiconductor device having a ferroelectric substance capacitor reducing influence of noise and being few in malfunctions. The semiconductor device includes a first capacitor formed on a surface of a semiconductor substrate and a second capacitor of a ferroelectric substance capacitance laminated on the first capacitor so as to connect in series.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device having aferroelectric substance capacitor, particularly to a structure for highintegration.

As high integration and michronization of semiconductor device advance,an occupying area of each part is decreased largely in LSI, and researchor providing as semiconductor mall and high in reliability is repeated.

In the semiconductor device having the ferroelectric substance capacitorbeing researched now, a capacitor using an ordinary insulating layer fordielectric substance layer such as a capacitor, called PIP capacitor,having an insulating layer between polysilicon layers, or a capacitor,called MOS capacitor, formed sandwiching a silicon oxide film between asilicon layer and metal is used greatly at the same time in order todetect reverse charge quantity of the ferroelectric substance capacitorand to convert to voltage.

That is, a ferroelectric substance capacitor C_(FERO) and PIP capacitorC_(PIP) are used greatly in series connection as shown in the equivalentcircuit of FIG. 7.

Conventionally, in order to realize such the semiconductor device, asshown in FIGS. 8A and 8B, a first capacitor is formed on an elementseparating insulating film 2 formed on surface of a silicon substrate 1and a second capacitor of a ferroelectric substance capacitor is formedso as to line with the first capacitor on the upper layer of the elementregion surrounded by the element separating insulating film 2. The firstcapacitor and the second capacitor are connected in series through awiring pattern connected mutually through contact holes.

Here, the first capacitor is constructed by a first electrode 3 of apolysilicon layer formed on the element separating insulating film 2, afirst insulating film 4 formed as two layers of a silicon oxide layerand a silicon nitride layer on the upper layer thereof, and a secondelectrode 5 of a polysilicon layer formed further the upper layerthereof.

The second capacitor is formed on the upper layer of the element regionsurrounded by the element separating insulating film as a not-commoncapacity, and the second capacitor includes a first electrode 7, aferroelectric substance film 8, and a second electrode 9.

The mutual connection of the first and second capacitors is achievedthrough a wiring pattern 10 connected through contact holes.

Such the capacitor structure has large occupying area and it has been alarge problem preventing michronization in LSI.

Further, there has been a problem that an escape route of noise is fewso as to receive easily influence of noise as a device as shown in aexplanation view of FIG. 9.

Thus, the conventional semiconductor device including the ferroelectricsubstance capacitor has large occupying area and it has been a largeproblem to prevent high integration of the device.

Further, the device easily receives influence of noise and it causesmalfunction.

SUMMARY OF THE INVENTION

The invention is performed in view of the circumstances, and an objectof the invention is to provide a semiconductor device having aferroelectric substance capacitor small in the occupying area and largein capacitance.

An another object of the invention is to provide a semiconductor devicehaving a ferroelectric substance capacitor reducing influence of noiseand being few in malfunctions.

The invention is characterized by including a first capacitor formed onsurface of a semiconductor substrate and a second capacitor of aferroelectric substance capacitance laminated on the first capacitor soas to connect in series.

According to such the construction, it is possible to reduce occupyingarea without reducing capacitance because the first capacitor and thesecond capacitor of the ferroelectric substance capacitor are stacked.Since long wiring is reduced in the semiconductor device, propagation ofnoise is reduced and it is possible to reduce malfunction.

Preferably, the invention is characterized by that the first capacitoris formed on an element separating insulating film.

According to such the construction, it is possible to use efficiently onthe element separating insulating film because the first and secondcapacitors are formed on the element separating insulating film. Sincethe capacitors are formed on the thick element separating insulatingfilm, it is possible to provide high LSI in reliability atmichronization without the element region in the substrate does notreceive bad reflection even at possible diffusion such as Pb or O₂ fromthe ferroelectric substance thin film.

Preferably, the invention is characterized by that the upper electrodeof the first capacitor and the lower electrode of the second capacitorare connected through plugs formed at an interlayer insulating film.

According to such the construction, the capacitor is high in reliabilitybecause the capacitor of laminating structure is formed using well aprocess for forming another element region.

Since the ferroelectric substance thin film or the ferroelectricsubstance capacitor and the electrode of the first capacitor areconnected through plugs without contacting directly, diffusion such asPb or O₂ from the ferroelectric substance thin film is cut off well onlyforming a barrier layer on the plug.

Preferably, the invention is characterized by connecting the upperelectrode of the first capacitor and the lower electrode of the secondcapacitor are connected through a wiring layer formed on the upper layeror the second capacitor.

According to such the construction too, it is possible to obtain alaminating layer capacitor including good series connecting body.

Preferably, the invention is characterized in that the upper electrodeof the first capacitor and the lower electrode of the second capacitorhave a common electrode, and that a capacitor insulating film for thefirst capacitor is arranged at the lower layer side of the commonelectrode and the ferroelectric substance film is arranged at upperlayer side.

According to Such the construction, since the upper electrode of thefirst capacitor and the lower electrode of the second capacitor have acommon electrode, forming of the electrode layer and the interlayerinsulating film is needless, and it is possible to provide asemiconductor device very simple and a little in difference of surfacelevel.

In the case using such the structure, although diffusion such as Pb orO₂ from the ferroelectric substance thin film becomes a problem, byusing high material in oxygen shielding effect such as two layersstructure film of iridium and iridium oxide as the common electrode,diffusion such as Pb or O₂ from the ferroelectric substance thin film isdepressed well, and it is possible to provide high device inreliability.

By adopting such the construction, floating capacitance removes and itis possible to design high driving speed.

Preferably, the invention is characterized in that the lower electrodeof the second capacitor includes the laminating film of iridium andiridium oxide.

According to such the construction, diffusion such as Pb or O₂ from theferroelectric substance thin film is depressed well, and it is possibleto provide high device in reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are views showing a semiconductor device of a firstembodiment of the invention;

FIG. 2 is a describing view showing propagation of noise of thesemiconductor device;

FIGS. 3A to 3E are views showing a process for manufacturing thesemiconductor device of a first embodiment of the invention;

FIGS. 4A and 4B are views showing the semiconductor device of the secondembodiment of the invention;

FIGS. 5A and 5B are views showing the semiconductor device of the thirdembodiment of the invention;

FIG. 6 is a describing view of the principle describing a method of thefourth embodiment of the invention;

FIG. 7 is a view showing an equivalent circuit of the invention;

FIGS. 8A and 8B are views showing the conventional semiconductor device;and

FIG. 9 is a describing view showing propagation of noise of theconventional semiconductor device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(Embodiment 1)

A semiconductor device having a PIP capacitor and a ferroelectricsubstance capacitor will be described for a first embodiment of theinvention. The semiconductor device includes a first capacitor C_(PIP)of a PIP capacitor formed on a surface of a semiconductor substrate anda second capacitor C_(FERO) Of a ferroelectric substance capacitorlaminated on the first capacitor C_(PIP) so as to connect thereto inseries as shown in FIG. 1A, a plane view, and 1B a sectional view cut byA—A line.

That is, as shown in FIGS. 1A and 1B, the second capacitor C_(FERO) ofthe ferroelectric substance capacitor is laminated on an elementseparating insulating film 2 formed on surface of a silicon substrate 1.The first capacitor and the second capacitor are connected in seriesthrough wiring pattern mutually connected through contact holes h3 toh4.

Here, the first capacitor is constructed by a first electrode 3 of apolysilicon layer formed on an element separating insulating film 2, afirst insulating film 4 formed on the first electrode 3 as two layers ora silicon oxide layer and a silicon nitride layer, and a secondelectrode 5 of a polysilicon layer further formed on the firstinsulating film 4.

The second capacitor is constructed by a first electrode 7 of two-layerfilm of iridium oxide and iridium formed through a first interlayerinsulating film 6 a covering the second electrode 5 of the firstcapacitor C_(PIP), a ferroelectric substance film 8 of PZT film formedon the first electrode thereof, and a second electrode 9 of two-layerfilm of iridium and iridium oxide formed on the ferroelectric substancefilm 8.

Further, the upper layer thereof is covered with a second interlayerinsulating film 6 b, mutual connection and taking out of the electrodeare performed at wiring patterns 10 a to 10 c formed on the secondinterlayer insulating film 6 b.

Here, the lower layer side electrode of the first capacitor, that is,the first electrode 3 is connected to the wiring pattern 10 b through afirst contact hole h1 formed through the first and the second interlayerinsulating films 6 a and 6 b, and is taken out to outside so as toconnect a ground wire.

The upper layer side electrode of the first capacitor, that is, thesecond electrode 5 is connected to the wiring pattern 10 c through acontact hole h4 formed through the first and the second interlayerinsulating films 6 a and 6 b, and is formed so as to contact the lowerlayer side electrode of the second capacitor, that is, the firstelectrode 7, through the third contact hole h3.

Further, the upper layer side electrode of the second capacitor, thatis, the second electrode is connected to the first wiring pattern 10 athrough the second contact hole h2 so as to connect to signal wire side.

According to such the construction, noise picked up by the firstelectrode of the first capacitor flows through the ground lineefficiently as it is, so it is possible that the capacitor hardlyreceives influence of the noise because the second electrode of thefirst capacitor and the first electrode of the second capacitor have thesame electric potential as shown in the describing view of FIG. 2.

Next, a process for manufacturing the ferroelectric substance capacitorwill be described with reference to FIGS. 3A to 3E.

First, the element separating insulating film 2 is formed on surface ofthe silicon substrate 1 by LOCOS method, a desired element region isformed in the element forming region surrounded with theelement,separating insulating film 2, and a polycrystal silicon film 3is formed on the element separating insulating film 2 by CVD method. Onthe surface thereof, a capacitor insulating film 4 or a laminating bodyof silicon oxide film and silicon nitride film is formed by thermaloxidation and CVD method, then, a polycrystal silicon film 5 is formedby CVD method. After that, patterning is performed by photography methodso as to form the first capacitor (FIG. 3A).

Continuously, a PSG film is formed for the first interlayer insulatingfilm 6 a.

After that, laminating film of iridium oxide and iridium is formedtargeting iridium by spattering method, and a first electrode 7 isformed by patterning the laminating film.

After that, a PZT film is formed on the first electrode 7 for aferroelectric substance film 8 by sol-gel method as shown in FIG. 3C.Mixed solution of Pb(CH₃COO)₂·3H₂O, Zr(t-OC₄H₉)₄, and Ti(i-OC₃H₇)₄ isused as a starting material. After spin coating the mixed solution, thefilm is dried at 150° C., and temporary baking of 400° C., 30 minutes isperformed at dry air atmosphere. After repeating this five times,thermal treatment of more than 700° C. is performed. Thus, theferroelectric substance film 8 of 250 nm is formed. Here, the PZT filmis formed placing 0.52 for x (PZT (52/48) hereafter) inPbZr_(x)Ti_(1−x)O₃.

Further, a laminating layer film of iridium oxide layer and iridiumlayer is formed on the ferroelectric substance film 8 by spatteringmethod (FIG. 3D). This laminating layer film of the iridium oxide layerand the iridium layer is formed to be the second electrode 9. Here, thesecond electrode 9 including the iridium oxide layer and the iridiumlayer is formed to have 200 nm thickness. Accordingly, the structurehaving ferroelectric substance capacitor as the second capacitorlaminated on the first capacitor is obtained.

A BPSG film is formed as the second interlayer insulating film 6 b, andthe contact holes h1 to h4 are formed by photolithography as shown inFIG. 3E.

W (tungsten) is filled in the contact holes by CVD method, Al (aluminum)layer is formed on surface of the substrate for wiring pattern, andfirst to third wiring patterns 10 a to 10 c are formed pattering byphotolithography so as to complete the semiconductor device of the firstembodiment of the invention shown in FIG. 1.

According to such the construction, the first and the second capacitorsare formed on the element separating insulating film 2, the upper partof the element separating insulating film is used efficiently for thecapacitor and it is possible to design large reduction of occupyingarea. Since the capacitor is formed on the thick element separatingfilm, the element region in the substrate does not receive bad influenceso as to provide a high LSI in reliability at michronization even ifthere is diffusion of Pb or O₂ from the ferroelectric substance thinfilm.

Since the ferroelectric substance thin film of the ferroelectricsubstance capacitor and the electrode of the first capacitor areconnected through plugs without contacting directly, diffusion of Pb orO₂ from the ferroelectric substance thin film is cut off well only byforming a barrier layer at the plug so that there is not possiblydeterioration caused by diffusion.

The LSI is possible to form very easily at manufacturing.

Since propagation of noise is reduced, it is possible to provide asemiconductor device a few in malfunctions.

When there is possibly diffusion of composing element of theferroelectric substance film, a barrier layer such as titanium, titaniumoxide, or titanium nitride lay be placed between the polycrystal siliconlayer constructing the plug and the first or the second electrode of thesecond capacitor. Thus, it is possible to obtain a semiconductor devicegood in working performance and high in reliability.

Further, the titanium layer has action as a junction layer. Adhesion ofiridium and silicon, or silicon oxide is not so good. Because of that,the layer comes off partly and there is possibly deterioration offerroelectric characteristics. However, in the embodiment, titaniumoxide layer acts as junction layer. Thus, not only there is diffusionpreventing effect to the silicon oxide of Pb or Zr, but also it ispossible to improve ferroelectric characteristics even by improvement ofadhesion.

(Embodiment 2)

Next, a second embodiment of the invention will be described withreference to FIGS. 4A and 4B, FIG. 4A is a plane view showing thesemiconductor device of the second embodiment of the invention, and FIG.4B is a sectional view cut by B—B line.

Although connection of the first capacitor and the second capacitor isperformed by the wiring pattern of surface of the substrate through thecontact hole formed at each electrode of each capacitor in the firstembodiment, in the embodiment, the second electrode 5 positioning at theupper layer side of the first capacitor by plugs constructed by thefourth contact hole h4 formed at the first interlayer insulating film 6a formed on the upper layer of the first capacitor and the firstelectrode 7 of the second capacitor just on the second electrode 5 areconnected after forming the first capacitor. Therefore, since electrodesare connected in the capacitor region, it is possible to designreduction of occupying area comparing the first embodiment.

Another construction is formed similarly as the first embodiment.

Forming the fourth contact hole and the plugs do not cause increase ofprocess by performing the same process as forming plugs such as tungstenplug at element region, and it is possible to realize michronization ofoccupying area.

(Embodiment 3)

Next, a third embodiment of the invention will be described withreference to FIGS. 5A and 5B. FIG. 5A is a plane view showing thesemiconductor device of the third embodiment or the invention, and FIG.5B is a sectional view cut by C—C line.

Although connection of the first capacitor and the second capacitor isperformed through the contact hole formed at each electrode of eachcapacitor in the first embodiment, in the embodiment, the upper portionelectrode of the first capacitor and the lower portion electrode of thesecond capacitor are constructed by a common electrode 11 of two-layerfilm of iridium and iridium oxide film. It is characterized that thecapacitor insulating film 4 for the first capacitor is arranged at lowerlayer side of the common electrode 11 and the ferroelectric substancefilm 8 of PZT is arranged on the common electrode 11.

According to such the construction, since the upper portion electrode ofthe first capacitor and the lower part electrode of the second capacitorare used for the common electrode, forming the electrode layer and theinterlayer insulating film is needless, so it is possible to provide asemiconductor device very simple and a little difference of surfacelevel.

Although diffusion of Pb and O₂ from the ferroelectric substance thinfilm 8 becomes problem in the case using such the structure, by usinghigh material in oxygen shielding effect such as two-layer structurefilm of iridium and iridium oxide as a common electrode, diffusion of Phand O₂ from the ferroelectric substance thin film layer is depressedwell, and it is possible to provide a high device in reliability.

(Embodiment 4)

Next, a fourth embodiment of the invention will be described.

Although the embodiment constructed PIP capacitor for the firstcapacitor in the first to the third embodiments, it is applicable in thecase using the MOS capacitor.

FIG. 6 is a view constructing the first capacitor with MOS capacitor.

A MOSFET as a switching transistor is formed at element regionsurrounded by the element separating insulating film 2 formed on surfaceof the silicon substrate. Second electrodes 15 of polycrystal siliconfilm is formed at one of source drain regions 13 a and 13 b of theMOSFET through a silicon oxide film 14 so as to form the MOS capacitor.At the upper layer thereof, a second capacitor is formed through athrough hole h4.

The second capacity constructed by a first electrode 7 or two-layer filmof iridium and iridium oxide, a ferroelectric substance film 8 of PZT,and second electrodes 9 of iridium and iridium oxide similarly as thefirst to the third embodiments.

Here, the MOSFET is constructed by the above source-drain regions 13 aand 13 b and a gate electrode of polycrystal silicon formed between theregions through the gate insulating film 16.

The MOSFET is formed similarly as the ordinal MOS process atmanufacturing.

The first capacitor may be formed so as to extend on the elementseparating insulating film.

The connection of the first and the second capacitors is changeablesimilarly as the first to third embodiments. When the upper layer sideelectrode of the first capacitor and the lower layer side electrode ofthe second capacitor are used as a common electrode like the structureof the third embodiment shown in FIGS. 5A and 5E, it is desirable toplace a barrier layer to prevent diffusion of Pb or O₂ included in theferroelectric substance film and desirable to use two-layer film ofiridium and iridium oxide for the electrode.

Although the first and the second electrodes of the second capacitor areconstructed by the laminating layer film of iridium and iridium oxide inthe embodiment, they may be two-layer film of platinum and iridium. Inthe case using plugs, there is a case that the film may be a singlelayer film.

Without limiting to titanium, the material withstanding following hightemperature process is selectable suitably for the barrier layer or theadhesive layer. The followings too are applicable: titanium, tantalum,zirconium, tungsten, these nitride, and nitride of high melting pointmetal containing aluminum or silicon such as TaAlN and TaSiN. Forexample, since TaAlN adding aluminum to TaN has characteristic beingeasy In etching and good in working performance, it is useful materialin the case needing patterning. Since TaSiN adding silicon to TaNcontains silicon, there are characteristics that preventing effect ofdiffusion of silicon from silicon oxide layer is high, etching is easycomparing with TaN, and working performance is good. Therefore, it isuseful material in the case needing patterning. Further, the TaSiNbecomes microcrystal or amorphous by adding Si so that barrierperformance improves.

Although PZT is used for the ferroelectric substance film 8 in eachembodiment, ferroelectric substance such as SBT or high permittivitydielectric such as BST is applicable.

Material characteristic of iridium is almost equal to the same ofplatinum. Resistivity of iridium is less than platinum and is desirablematerial for electrode. Resistivity of iridium oxide is 49×10⁻⁶ Ωcm, sothere is no problem as material of the electrode.

Although iridium permeates through oxygen in the ferroelectric substancefilm 5 because of crystallization of column shape, two-layer film ofiridium and iridium oxide or two-way film covering the upper layer ofiridium with Pt is used in the embodiment. Since the iridium oxidehardly permeates through oxygen because of not having crystal structure,of column shape, shortage of oxygen of the ferroelectric substance filmcan be prevented. For preventing oxidation of iridium, it is desirableto form a platinum layer on the surface, however it may not be formed.Although there is high possibility that whole of the electrode becomeiridium oxide layer at oxidation of iridium, the iridium oxide layer isconductive and has a fine film structure to prevent permeation of oxygenand like so as to act well as an oxidation preventing film.

As described above, since the first capacitor and the second capacitorof the ferroelectric substance capacitor are laminated, reduction ofoccupying area can be designed without reducing capacity. Since drawingof long wiring is reduced in the semiconductor device, propagation ofnoise can be reduced and it is possible to design reduction ofmalfunction.

What is claimed is:
 1. A semiconductor device comprising: a firstcapacitor formed on a surface of a semiconductor substrate; and a secondcapacitor of the ferroelectric substance capacitance laminated on thefirst capacitor to be serially connected with the first capacitor,wherein an upper electrode of the first capacitor and a lower electrodeof the second capacitor are connected through a wiring layer formedabove the second capacitor, and a lower electrode of the first capacitorand the lower electrode of the second capacitor overlap vertically. 2.The semiconductor device as claimed in claim 1, wherein the firstcapacitor is formed on an element separating insulating film.
 3. Thesemiconductor device as claimed in claim 1, wherein a lower electrode ofthe second capacitor includes the laminating film of iridium and iridiumoxide.
 4. A semiconductor device comprising: a first capacitor formed ona surface of a semiconductor substrate; and a second capacitor of theferroelectric substance capacitance laminated on the first capacitor tobe serially connected with the first capacitor; a common electrode, thecommon electrode forming an upper electrode of the first capacitor and alower electrode of the second capacitor; a capacitor insulating film ofthe first capacitor provided below the common electrode; and aferroelectric substance film of the second capacitor provided on thecommon electrode, wherein a lower electrode of the first capacitor andthe lower electrode of the second capacitor overlap vertically.
 5. Thesemiconductor device as claimed in claim 4, wherein the first capacitoris formed on an element separating insulating film.